One of the alluring aspects of examining the role of chromatin modifications in modulating transcription required for drug seeking behavior is that these modifications may provide transient and potentially stable epigenetic marks in the service of activating and/or maintaining transcriptional processes. These in turn may ultimately participate in the molecular mechanisms required for neuronal changes subserving long lasting changes in behavior. As an epigenetic mechanism of transcriptional control, chromatin modification has been shown to participate in maintaining cellular memory (e.g., cell fate) and may underlie the strengthening and maintenance of synaptic connections required for long-term changes in behavior. Epigenetics has become central to several fields of neurobiology where researchers have found that regulation of chromatin modification has a significant role in epilepsy, drug addiction, depression, neurodegenerative diseases, and memory. The research in this proposal is focused on histone deacetylation, which is a mechanism by which gene expression is silenced. Histone deacetylases are key negative regulators of long-term memory formation, but their role in drug seeking behavior remains largely unexplored. The focus of Aim 1 of this grant proposal is to examine the role of histone deacetylase (HDAC) 3 in the acquisition of cocaine-induced conditioned place preference. HDAC3 is the most abundant class I HDAC expressed in brain. The approach involves genetically modified HDAC3-FLOX mice in which homozygous HDAC3 deletions can be generated using adeno-associated virus (AAV) expressing Cre recombinase. This method allows for the generation of spatially and temporally restricted HDAC3 deletions that avoid developmental and performance issues that arise from traditional knockout mice or even most transgenic mice. The focus of Aim 2 is to examine the ability of a novel class of HDAC inhibitors that are selective for specific HDACs to facilitate extinction of drug seeking behavior. In both aims, histone modifications in brain sections will be examined using epifluorescent microscopy, which allows one to determine how HDAC3 directly/indirectly regulates several histone modifications of interest at the level of individual neurons. In summary, this research proposal describes an innovative genetic and pharmacological approach to examine the role of a key HDAC, HDAC3, in acquisition and extinction of drug-seeking behavior.